A probe assembly and/or method for characterizing electrical conductivity of a conducting layer that is buried below an insulating layer, such as in transistor substrates in semiconductor industry, is provided herein. Alternatively, one or more embodiments described herein may be used for other types of substrates or devices.
Diffused metal contacts are used for some known four-point electrical characterization methods for buried (e.g., not exposed) conducting layers. These methods, however, may require the use of alloyed ohmic contacts with the buried conducting layers, which can be problematic. Such ohmic contacts may be problematic in low-density systems (e.g., samples under test or examination that have relatively low carrier density in a semiconductor body or layer in which the buried conducting layer is disposed) and can take considerable time to fabricate. Additionally, such contacts may require different alloy recipes for the ohmic contacts used in n- and p-type doped systems (e.g., n- and p-type doped semiconductor or insulator samples). For some relatively new materials (e.g., recently developed materials) used in the samples having the buried conducting layers, the recipes for creating alloy recipes for the ohmic contacts may have not yet been developed yet. Moreover, alloyed ohmic contacts can be permanent such that, once a sample is used for characterization purposes, the sample cannot be reused. The sample may be destroyed or otherwise altered in such a manner to provide the ohmic contacts with the buried conducting layer that the sample may not be able to be reused for one or more other (e.g., intended) purposes.
Some known probe stations can be used for four-point electrical characterization methods of semiconductor or nonconducting samples having the buried conducting layers, but these stations may require pre-fabrication processing of the sample in order to expose the buried conducting layer engagement with the probes of the station. Additionally, the sample may not be reused after characterization due to scratching of the sample with the probes during examination of the sample. Moreover, the probes can eventually wear down due to the repeated physical contact with the samples.